Through my experience these are a few things that get overlooked and are also
hard to inspect properly if not impossible when viewing a mkiv.
Brake calipers are prone to seizing due to the outer seals getting old
and splitting, this is on both the smaller (j spec sliding calipers) &
(larger uk spec opposed piston calipers)
Brake & fuel pipes corroding especially at the rear where their fairly difficult
to check properly
Radiators, heater matrix, ac rad, UK spec diff cooler, SMIC's on turbo cars
Seizing and or worn suspension bushes, can be costly to fix as they can be very difficult
to remove and OE parts are expensive. (rear upper arm = £450 each)
Dampers will be tired
Front cross member under the radiator is a common area to suffer from corrosion.
Front crank seals seem to be a common problem these days.
Crank pulleys splitting in two, there a bonded harmonic damper
Any rubber hoses will be very tired in the engine bay but not
to bad to replace with silicon or hose from local car spares shops
Valve stem seals, cam cover seals.
Coil pack connectors on turbo cars